1. Field of the Invention
The present invention relates to methods of joining metal components, more particularly to a method of joining metal components involving welding the components together and inserting an adhesive between the welded components.
2. Prior Art
Metal components are conventionally joined together in a variety of techniques including fusion welding, solid state bonding, chemical/mechanical bonding and mechanical engagement and locking. In fusion welding, the components are joined together through coalescence of molten metals. A weld between the components occurs when the molten metals of the components intermix and solidify. Conventional processes which are based upon fusion welding include gas metal arc welding (e.g. gas tungsten arc welding) and laser beam welding. In solid-state joining of metal components, interfacial diffusion between the mating surfaces is achieved by forcing the parts together under pressure and application of heat at the interface between the components or forcing together simultaneously plasticized metals such as in friction stir welding and forging. Chemical/mechanical bonding of metal components includes the use of adhesives, mechanical engagement of locking of components such as via bolts, rivets, and other such fasteners.
In certain circumstances where structural redundancy is important or additional sealing is required between the two components, two of these joining processes may be combined to impart their particular beneficial characteristics to the overall performance of the joint. This approach of using two joining processes has been utilized in the aerospace, automotive and transportation industries. Typically, mechanical fasteners are used to join components along with adhesives or sealants. Such joints that include mechanical fasteners and adhesives have been strong and reliable.
However, a combination of fusion and solid state based welding processes with chemical/mechanical bonding processes (e.g., using adhesives) has been problematic. Metallurgical incompatibilities arise when these two processes are applied either simultaneously at the same joining area or even when the two processes are performed sequentially. Contact between adhesive (typically an organic material) and hot molten plasticized metals, which form during welding, results in serious damage to the integrity of both the welded joint and the adhesive bond. In some instances, contact between the molten metal of the weld and the adhesive causes the adhesive to violently disintegrate into hydrocarbonaceous fumes which disrupts the stability of the welding process (such as the welding arc, laser beam generated plasma over a keyhole and molten pool), introduces contaminants into solidifying welds (producing gross open and bulk pores, craters, inclusions and excessive crud on the surface) and leads to inconsistent weld geometries. If an adhesive is applied while welding is occurring, the weld may become displaced or change shape by the fumes erupting from the adhesive, become petrified in distinct locations or develop uncontrolled pores and skips, all of which lead to compromised joint quality and uniformity. When hot plasticized metal contacts an adhesive, some of the adhesive may be incorporated into the metal and distributed as continuous (e.g. films) or fragmented contaminants throughout the weld.
Accordingly, a need remains for a method of joining metal components using fusion or solid state welding along with adhesive bonding which avoids these problems.